1. Field of the Invention
The present invention relates generally to the design and use of medical devices, and more particularly to the design and use of an implantable port for establishing temporary access to a patient's vascular system for hemodialysis and other extracorporeal blood treatments. Access to a patient's vascular system can be established by a variety of temporary and permanently implanted devices. Most simply, temporary access can be provided by the direct percutaneous introduction of a needle through the patient's skin and into a blood vessel. While such a direct approach is relatively simple and suitable for applications, such as intravenous feeding, intravenous drug delivery, and other applications which are limited in time, they are not suitable for hemodialysis and other extracorporeal procedures that must be repeated periodically, often for the lifetime of the patient.
For hemodialysis and other extracorporeal treatment regimens, a variety of implantable ports have been proposed over the years. Typically, the port includes a chamber on an access region, such as a septum, and the chamber is attached to an implanted catheter which in turn is secured to a blood vessel. In the case of veins, the catheter is typically indwelling and in the case of arteries, the catheter may be attached by conventional anastomosis.
Of particular interest to the present invention, implantable ports typically include a needle-penetrable septum which permits the percutaneous penetration of a needle into the internal chamber. The chamber, in turn, is connected to one end of the catheter, and the other end of the catheter is indwelling in the blood vessel. While workable, such designs suffer from a number of problems. Repeated penetration of the septum often leads to degradation over time, presenting a substantial risk of small particulates entering the blood stream and/or need to periodically replace the port. Second, the passage of blood through the chamber or plenum will often encounter regions of turbulence or low flow, either of which can degrade the quality of blood over time. Third, many previous vascular access ports have failed to provide an internal valve structure which isolates the interior of the port from the lumen of the implanted catheter when the port is not in use. Fourth, in previous ports which employ a valve, self-penetrating needles are not used since they will be damaged by and/or cause damage to the port. In such instances, it is frequently necessary to use a catheter combined with a removable stylet, which is both more costly and more inconvenient than use of a simple needle. Fifth, in ports which employ either septums or valves, the needle or other access device is prone to accidental dislodgement. Loss of a needle from a blood return port is particularly dangerous since blood may continue to be withdrawn while it is simultaneously being lost to the environment. While needle and port designs have been proposed for preventing such accidental dislodgement, most such designs are complex and are not themselves fail safe.
A number of vascular access designs have been proposed which address at least some of the problems. In particular, a series of issued U.S. Patents which name William Ensminger as an inventor disclose access ports having internal lumens for receiving a percutaneously introduced access device (e.g. a needle or catheter/stylet combination) and internal valve structures for isolating the port from an associated implanted catheter. These patents, which are listed herein below, disclose a number of specific valve types which may be incorporated within the access port, including leaflet valves, ball valves, flapper valves, and other specific configurations which are referred to as "articulating valves." All such structures, however, generally require that the access device be passed through the valve itself (i.e., the portion which closes the blood flow path through the valve) in order to cause the valve to open. Such a requirement presents the risk that the valve will be degraded by direct contact with the access device after repeated uses so that portions of the valve may be degraded and released into circulation. Such valves also present a significant risk of failure after repeated use or contact with a sharpened needle. Additionally, such valve structures can damage the access device as it is being introduced therethrough, thus potentially disrupting valve flow through the needle during a subsequent treatment protocol.
An additional problem with the valves of Ensminger is that the entry ports are usually inclined at a substantial angle relative to the skin surface through which the access device is introduced. Such angled access requires that the personnel introducing the access device guess the angle and estimate the optimum insertion point on the patient's skin. Such uncertainty in the device penetration is perhaps why the Ensminger designs all require the use of enlarged "funnel" for receiving and aligning the needle as it is introduced. It would thus be advantageous to provide access ports having entry passages which are disposed generally "vertically" (i.e., at an angle which is substantially normal to the skin surface through which the needle is being introduced). By penetrating the needle "straight in," it is much easier to align the needle with the target orifice and the size of the orifice (needle penetration) area can be reduced.
For these reasons, it would be desirable to provide improved implantable access ports for percutaneously accessing a patient's blood vessels, including both arteries and veins. The access ports preferably will comprise a valve structure for isolating the port from an associated implanted catheter when the port is not in use. The valve will preferably provide little or no structure within the blood flow lumen of the access port and will even more preferably not require passage of a needle or other access tube through the seating portion of a valve in order to open the valve. Furthermore, the port structure including the valve elements therein will have a substantially uniform cross-sectional area and will present no significant constrictions or enlargements to disturb fluid flow therethrough. Preferably, the port designs will permit percutaneous access using a conventional needle, such as a fistula needle, without damage to either the port or the needle. Still more preferably, the needles or other devices used to access the port will resist accidental dislodgement from the port without requiring significant extra structure or additional components. Ports and valves according to the present invention will meet at least some of these objectives.
2. Description of the Background Art
U.S. Pat. No. 5,562,617 and WO 95/19200, assigned to the assignee of the present application, describe implantable vascular access systems comprising an access port having an internal slit or duck bill valve for preventing back flow into the port. Vascular access ports having various articulating valves for isolating the port from the vascular system in the absence of external percutaneous connection to the port are described in the following U.S. Patents which name William Ensminger as an inventor: U.S. Pat. Nos. 5,527,278; 5,527,277; 5,520,643; 5,503,630; 5,476,451; 5,417,656; 5,350,360; 5,281,199; 5,263,930; 5,226,879; 5,180,365; 5,057,084; and 5,053,013. Other patents and published applications which show implantable ports having valve structures opened by insertion of a needle include U.S. Pat. Nos. 4,569,675; 4,534,759; 4,181,132; 3,998,222; and WO 96/31246. U.S. Pat. No. 5,637,088 describes a septum-type implantable port which employs a dual needle to help prevent dislodgement.